1. Technical Field
This disclosure relates to semiconductor fabrication and more particularly, to an improved method and apparatus for in-situ parameter measurement and control to provide improved yield.
2. Description of the Related Art
Semiconductor processing involves maintaining a controlled environment for various fabrication steps. Semiconductor wafers are typically placed inside a chamber and exposed to various temperature and pressure conditions. During fabrication, control of these parameters impacts chip yield. Temperature differences across the wafer lead to process nonuniformity and result in yield loss.
Temperature is typically measured on the wafer using temperature dots or thermocouples. Temperature dots are fixed on the wafer and give a rough estimate of the temperature distribution across the wafer. Temperature dots do not generally measure the temperature at the surface of the wafer. Further, temperature dots have a resolution of only .+-.5.degree. C. To effectively use temperature dots, it is often necessary to perform many trials to get a timely resolved temperature measurement. Even then, the temperature is not determined over the full wafer. A maximum temperature is reached and recorded by the temperature dots, but there is no time resolution of when the maximum temperature was reached. Thermocouples must be mounted on the wafer and suffer from the same deficiencies as temperature dots.
A "charm" wafer is commercially available from Wafer Charging Monitors, Inc. The "charm" wafer measures only peak values for temperature and therefore does not provide timely information since peak values could occur at various times during processing.
Therefore, a need exists for an apparatus and method for determining temperature at a wafer surface which is accurate and reliable. A further need exists for an apparatus and method for determining temperature for different chamber and/or chuck configurations.